Solid-Phase Epitaxy of Perovskite High Dielectric PrAlO₃ Films Grown by Atomic Layer Deposition for Use in Two-Dimensional Electronics and Memory Devices

Abstract

An atomic layer deposition (ALD) process is reported for the growth of nanoscale PrAlO3 thin films for two-dimensional electronics and memory device applications using tris­(isopropyl­cyclopentadienyl)­praseodymium (Pr­(C5H4 iPr)3), trimethyl­aluminum (AlMe3), and water. Pr­(C5H4 iPr)3 was first evaluated as a precursor for the formation of thin films of the binary oxide Pr2O3 by using water as the coreactant. Self-limited growth of Pr2O3 was demonstrated for pulse lengths of ≥3 s, with a growth rate of ∼0.85 Å/cycle. The ALD growth of PrAlO3 films was examined on Si, thermal SiO2, and (001)-oriented SrTiO3 substrates. Self-limited growth was demonstrated for Pr­(C5H4 iPr)3, AlMe3, and water at 300 °C by using a 1:1 ratio of the number of Pr­(C5H4 iPr)3 and AlMe3 pulses. An ALD window was observed from 275 to 325 °C with a growth rate of ∼1.7 Å/cycle. The as-deposited PrAlO3 films on all substrates were amorphous, had smooth surfaces, and contained <0.5% carbon, as analyzed by grazing incidence wide-angle X-ray scattering, X-ray reflectivity, and X-ray photoelectron spectroscopy, respectively. Films grown with a 1:1 ratio of Pr­(C5H4 iPr)3 and AlMe3 pulses were aluminum-rich (Pr:Al ∼ 1:1.2–1.4). Heating PrAlO3 layers deposited on SrTiO3 to 800 °C for 3 h resulted in fully crystallized PrAlO3 films. The crystallized PrAlO3 films were highly (001)-oriented. The PrAlO3 00L and SrTiO3 00L reflections appeared on the same rod of reciprocal space, further indicating that the amorphous PrAlO3 film transforms into an epitaxial layer. The rocking curve width of the PrAlO3 (001) reflection was 7°. By contrast, PrAlO3 films deposited on Si substrates with native oxide remained amorphous after annealing at 1000 °C for 8 h. The difference in the crystallization between PrAlO3 layers deposited on crystalline SrTiO3 and amorphous native SiO2 substrates indicates that PrAlO3 on SrTiO3 crystallized by solid-phase epitaxy, in which the nucleation and orientation of the crystallized layer are set by the atomic configuration at the substrate–film interface.

Antimicrobial Bilayer Nanocomposites Based on the Incorporation of As-Synthetized Hollow Zinc Oxide Nanotubes

“…One of the advantages that most attracts the attention of this technique is the ability to generate a unique uniform deposition, which allows the thickness of the film to be controlled by the amount of ALD cycles and, in addition, complex three-dimensional surfaces can be uniformly coated. These characteristics give it a great versatility that have allowed its application in a wide variety of areas, such as microelectronics, energy storage systems, water treatment, catalysis, and medicine and biology [21][22][23][24][25][26][27][28][29]. Nevertheless, the combination of EP and ALD has been scarcely used to synthesize nanoparticles with antimicrobial purposes.…”

Oxidic 2D Materials

“…Thin films could be used, for example, in piezoelectric applications such as pressure sensors [310], transducers [311], high-voltage generators [312] and nonlinear energy harvesters [313], meeting demands for minimal dimensions, weight reduction and lower energy consumption. Similarly, 2D electronics like high-power transistors or ferroelectric capacitors and memory device applications are conceivable [104,314,315]. Challenges such as defect structure, processability and long-term stability of the devices must first be solved to fully exploit the potential of ultra-thin heterostructures and enable their use as transistors, semiconductor circuits or flexible and transparent electronics [240].…”

Reduction of Interface Reactions in the Low-Temperature Solid-Phase Epitaxy of ScAlMgO4 on Al2O3(0001)

“…The surface and bulk diffusion responsible for large-scale morphological effects and crystal growth can be expected to have different activation energies, and it is possible that diffusion will be suppressed as the temperature decreases before crystallization slows to an impractical speed. A second indication that low-temperature methods may yield a route to the formation of ScAlMgO 4 without interfacial reactions is that recent results in other compounds indicate that crystal growth via SPE can occur in complex oxides at far lower temperatures than those previously employed in ScAlMgO 4 epitaxy. , SPE in the homoepitaxy of SrTiO 3 on SrTiO 3 , for example, occurs at rates on the order of 1 nm min –1 at 450 °C . Slightly higher temperatures on the order of 800 °C induce heteroepitaxial crystallization in PrAlO 3 on SrTiO 3 .…”

“…A second indication that low-temperature methods may yield a route to the formation of ScAlMgO 4 without interfacial reactions is that recent results in other compounds indicate that crystal growth via SPE can occur in complex oxides at far lower temperatures than those previously employed in ScAlMgO 4 epitaxy. , SPE in the homoepitaxy of SrTiO 3 on SrTiO 3 , for example, occurs at rates on the order of 1 nm min –1 at 450 °C . Slightly higher temperatures on the order of 800 °C induce heteroepitaxial crystallization in PrAlO 3 on SrTiO 3 . Lower temperatures than those previously employed in the crystallization of ScAlMgO 4 can in principle simultaneously reduce the rate of interfacial reactions and limit the atomic transport responsible for the development of three-dimensional crystalline morphologies.…”

“…A second indication that low-temperature methods may yield a route to the formation of ScAlMgO 4 without interfacial reactions is that recent results in other compounds indicate that crystal growth via SPE can occur in complex oxides at far lower temperatures than those previously employed in ScAlMgO 4 epitaxy. 18,19 SPE in the homoepitaxy of SrTiO 3 on SrTiO 3 , for example, occurs at rates on the order of 1 nm min −1 at 450 °C. 19 Slightly higher temperatures on the order of 800 °C induce heteroepitaxial crystallization in PrAlO 3 on SrTiO 3 .…”